Vojnosanitetski pregled 2013 Volume 70, Issue 3, Pages: 298-303
https://doi.org/10.2298/VSP1303298M
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Changes in motor cortex excitability associated with muscle fatigue in patients with Parkinson's disease
Milanović Slađan (Institute for Medical Research, Belgrade)
Filipović Saša R. (Institute for Medical Research, Belgrade)
Radovanović Saša (Institute for Medical Research, Belgrade)
Blesić Suzana (Institute for Medical Research, Belgrade)
Ilić Nela V. (Clinical Center of Serbia, Clinic of Rehabilitation Medicine, Belgrade)
Kostić Vladimir S. (Clinical Center of Serbia, Neurology Clinic, Belgrade + Faculty of Medicine, Belgrade)
Ljubisavljević Miloš R. (Institute for Medical Research, Belgrade)
Background/Aim. Transcranial magnetic stimulation (TMS) is a standard
technique for noninvasive assessment of changes in central nervous system
excitability. The aim of this study was to examine changes in responses to
TMS in patients suffering from Parkinson’s disease (PD) during sustained
submaximal isometric voluntary contraction [60% of maximal voluntary
contraction (MVC)] of the adductor pollicis muscle, as well as during a
subsequent recovery period. Methods. Cortical excitability was tested by
single TMS pulses of twice of the motor threshold intensity applied over the
vertex. Testing was carried out during the sustained contraction phase every
10 s before and every 5 s after the endurance point, as well as at rest and
during brief 60% MVC contractions before (control), immediately after the
sustained contraction, and at 5 min intervals during the recovery period.
Results. Although the PD patients could sustain the contraction at the
required level for as long period of time as the healthy subjects (though
contraction level subsided more rapidly after the endurance point), effects
of muscle fatigue on the responses to TMS were different. In contrast to the
findings observed in the healthy people where motor evoked potentials (MEP)
and EMG silent period (SP) in fatigued muscle gradually diminished during
contraction up to the endurance point, and increased thereafter, in the
majority of patients no changes occurred in MEP size (peak and area) of the
adductor pollicis muscle, either before or after the endurance point. On the
other hand, changes in the SP of this muscle differed among the subjects,
showing a gradual increase, a decrease or no changes in duration. The trends
of changes in both MEP size and SP duration in the musculus brachioradialis
varied among the tested PD patients, without any consistent pattern, which
was in contrast with the findings in the healthy people where both measures
showed a gradual increase from the beginning of the sustained contraction. A
complete dissociation between changes in MEP and SP during fatigue was also
of note, which differed sharply from the findings in the healthy people in
who fatigue induced changes in these measures followed identical patterns.
Conclusion. These results in the PD patients suggest the presence of
impairment and/or compensatory changes in mechanisms responsible for
adaptation of voluntary drive as well as for matching between cortical
excitation and inhibition which become manifest in demanding motor tasks such
as those imposed by muscle fatigue.
Keywords: muscle fatigue, Parkinson disease, motor cortex, transcranial magnetic stimulation